I have been using Database First Entity Framework (EDMX) and SQL Server Data Tools Database Projects in combination very successfully - change the schema in the database and 'Update Model from Database' to get them into the EDMX. I see though that Entity Framework 7 will be dropping the EDMX format and I am looking for a new process that will allow me to use Code First in Combination with Database Projects.
Lots of my existing development and deployment processes rely on having a database project that contains the schema. This goes in source control is deployed along with the code and is used to update the production database complete with data migration using pre and post deployment scripts. I would be reluctant to drop it.
I would be keen to split one big EDMX into many smaller models as part of this work. This will mean multiple Code First models referencing the same database.
Assuming that I have an existing database and a database project to go with it - I am thinking that I would start by using the following wizard to create an initial set of entity and context classes - I would do this for each of the models.
Add | New Item... | Visual C# Items | Data | ADO.NET Entity Data Model | Code first from database
My problem is - where do I go from there? How do I handle schema changes? As long as I can get the database schema updated, I can use a schema compare operation to get the changes into the project.
These are the options that I am considering.
Make changes in the database and use the wizard from above to regenerate. I guess that I would need to keep any modifications to the entity and/or context classes in partial classes so that they do not get overwritten. Automating this with a list of tables etc to include would be handy. Powershell or T4 Templates maybe? SqlSharpener (suggested by Keith in comments) looks like it might help here. I would also look at disabling all but the checks for database existence and schema compatibility here, as suggested by Steve Green in the comments.
Make changes in code and use migrations to get these changes applied to the database. From what I understand, not having models map cleanly to database schemas (mine don't) might pose problems. I also see some complaints on the net that migrations do not cover all database object types - this was also my experience when I played around with Code First a while back - unique constraints I think were not covered. Has this improved in Entity Framework 7?
Make changes in the database and then use migrations as a kind of comparison between code and the database. See what the differences are and adjust the code to suit. Keep going until there are no differences.
Make changes manually in both code and the database. Obviously, this is not very appealing.
Which of these would be best? Is there anything that I would need to know before trying to implement it? Are there any other, better options?
So the path that we ended up taking was to create some T4 templates that generate both a DbContext and our entities. We provide the entity T4 a list of tables from which to generate entities and have a syntax to indicate that the entity based on one table should inherit from the entity based on another. Custom code goes in partial classes. So our solution looks most like my option 1 from above.
Also, we started out generating fluent configuration in OnModelCreating in the DbContext but have swapped to using attributes on the Entities (where attributes exist - HasPrecision was one that we had to use fluent configuration for). We found that it is more concise and easier to locate the configuration for a property when it is right there decorating that property.
Related
Is there a way to combine code-first and database-first in the same context? We are running into massive development-time performance problems when editing the EDMX file (it takes 1.5 minutes to save). I've moved our non-insert/update/delete UDFs/stored procs to some custom T4 templates that automatically generate model-first code, but I can't seem to get OnModelCreating to be called when EDMX is involved.
Other things we've considered, but won't work for one reason or another:
We can't (reasonably) separate our code to multiple contexts as there is a lot of overlap in our entity relationships. It also seems like quite a people who have gone this route regret it.
We tried having 2 different contexts, but there are quite a few joins between Entities & UDFs. This may be our last hope, but I'd REALLY like to avoid it.
We can't switch to Dapper since we have unfortunately made heavy use of IQueryable.
We tried to go completely to Code-First, but there are features that we are using in EDMX that aren't supported (mostly related to insert/update/delete stored procedure mapping).
Take a look at the following link. I answered another question in a similar fashion:
How to use Repository pattern using Database first approach in entity framework
As I mentioned in that post, I would personally try to switch to a Code First approach and get rid of the EDMX files as it is already deprecated and most importantly, the maintenance effort is considerable and much more complex compared with the Code First approach.
It is not that hard switching to Code First from a Model First approach. Some steps and images down below:
Display all files at the project level and expand the EDMX file. You will notice that the EDMX file has a .TT file which will have several files nested, the Model Context and POCO clases between them as .cs or .vb classes (depending on the language you are using). See image down below:
Unload the project, right click and then edit.
See the image below, notice the dependencies between the context and the TT file
Remove the dependencies, the xml element should look like the image below:
Repeat the procedure for the Model classes (The ones with the model definition)
Reload your project, remove the EDMX file(s)
You will probably need to do some tweeks and update names/references.
I did this a few times in the past and it worked flawlessly on production. You can also look for tools that do this conversion for you.
This might be a good opportunity for you to rethink the architecture as well.
BTW: Bullet point 4 shouldn't be a show stopper for you. You can map/use Stored Procedures via EF. Look at the following link:
How to call Stored Procedure in Entity Framework 6 (Code-First)?
It also seems like quite a people who have gone this route [multiple contexts] regret it.
I'm not one of them.
Your core problem is a context that gets too large. So break it up. I know that inevitably there will be entities that should be shared among several contexts, which may give rise to duplicate class names. An easy way to solve this is to rename the classes into their context-specific names.
For example, I have an ApplicationUser table (who hasn't) that maps to a class with the same name in the main context, but to a class AuthorizationUser in my AuthorizationContext, or ReportingUser in a ReportingContext. This isn't a problem at all. Most use cases revolve around one context type anyway, so it's impossible to get confused.
I even have specialized contexts that work on the same data as other contexts, but in a more economical way. For example, a context that doesn't map to calculated columns in the database, so there are no reads after inserts and updates (apart from identity values).
So I'd recommend to go for it, because ...
Is there a way to combine code-first and database-first in the same context?
No, there isn't. Both approaches have different ways of building the DbModel (containing the store model, the class model, and the mappings between both). In a generated DbContext you even see that an UnintentionalCodeFirstException is thrown, to drive home that you're not supposed to use that method.
mostly related to insert/update/delete stored procedure mapping
As said in another answer, mapping CUD actions to stored procedures is supported in EF6 code-first.
I got here from a link in your comment on a different question, where you asked:
you mentioned that code-first & database-first is "technically possible" could you explain how to accomplish that?
First, the context of the other question was completely different. The OP there was asking if it was possible to use both database-first and code-first methodologies in the same project, but importantly, not necessarily the same context. My saying that it was "technically possible" applies to the former, not the latter. There is absolutely no way to utilize both code-first and database-first in the same context. Actually, to be a bit more specific, let's say there's no way to utilize an existing database and also migrate that same database with new entities.
The terminology gets a bit confused here due to some unfortunate naming by Microsoft when EF was being developed. Originally, you had just Model-first and Database-first. Both utilized EDMX. The only difference was that Model-first would let you design your entities and create a database from that, while Database-first took an existing database and created entities from that.
With EF 4.1, Code-first was introduced, which discarded EDMX entirely and let you work with POCOs (plain old class objects). However, despite the name, Code-first can and always has been able to work with an existing database or create a new one. Code-first, then is really Model-first and Database-first, combined, minus the horrid EDMX. Recently, the EF team has finally taken it a step further and deprecated EDMX entirely, including both the Model-first and Database-first methodologies. It is not recommended to continue to use either one at this point, and you can expect EDMX support to be dropped entirely in future versions of Visual Studio.
With all that said, let's go with the facts. You cannot both have an existing database and a EF-managed database in a single context. You would at least need two: one for your existing tables and one for those managed by EF. More to the point, these two contexts must reference different databases. If there are any existing tables in an EF-managed database, EF will attempt to remove them. Long and short, you have to segregate your EF-managed stuff from your externally managed stuff, which means you can't create foreign keys between entities in one context and another.
Your only real option here is to just do everything "database-first". In other words, you'll have to just treat your database as existing and manually create new tables, alter columns, etc. without relying on EF migrations at all. In this regard, you should also go ahead and dump the EDMX. Generate all your entities as POCOs and simply disable the database initializer in your context. In other words, Code-first with an existing database. I have additional information, if you need it.
Thank you to everyone for the well thought out and thorough answers.
Many of these other answers assume that the stored procedure mappings in EF Code-First work the same, but they do not. I'm a bit fuzzy on this as it's been about 6 months since I looked at it, but I believe as of EF 6.3 code first stored procedures require that you pass every column from your entity to your insert/update stored procedure and that you only pass the key column(s) to your delete procedure. There isn't an option to pick and choose which columns you can pass. We have a requirement to maintain who deleted a record so we have to pass some additional information besides just a simple key.
That being said, what I ended up doing was using a T4 template to automatically generate my EDMX/Context/Model files from the database (with some additional meta-data). This took our developer time experience down from 1.5 minutes to about 5 seconds.
My hope is EF stored procedure mappings will be improved to achieve parody with EDMX and I can then just code-generate the Code-First mappings and remove the EDMX generation completely.
I have code first classes which are generated from my existing db using ADO.NET Entity Data Model. Now I've added some new tables to the database.
I want to know if its possible to create associated code classes from the new db tables without (re)creating the model again from scratch?
Yes it is, if you use Reverse Engineer Code First to do so. It will create POCOs exactly like Code-First, but it will do so based completely on the current database. No .edmx file and no T4 template. Just Code-First.
You should know, by the way, that this (along with regular Code-First) are going to be the only ones allowed in EF7. They are getting rid of many things to try to slim it down, and both Model- and Database-First got the ax (at least, for now). This blog post from Microsoft's ADO.NET blog explains that, along with some other features.
We are starting a new large corporate project. The database will be 100+ tables and we will be using Entity Framework, Web API and MVC.
My question is specifically related to the Entity Framework aspects of the solution.
I am trying to make a choice between the following:
Code first to an existing Database
EF Designer to an Existing Database (Database First)
I know we can use EF to generate the database from code first or from the EF designer, but we prefer to have full control over the database and develop that in the traditional way, so we have excluded the EF options that allow us to auto-generate the database.
Most of what I can find on the internet relating to Code First deals with creating a new database and then using code migrations. And when the discussions deal with Database first then the discussions favour the EF Designer. Example here: Code-first vs Model/Database-first
My preference is to go with the combination of Code First to an existing database.
The following are my considerations for favouring this option and I'm wondering if there is anything else I need to consider, and whether my assumptions/thoughts are correct.
Code first to an Existing database
There will be a large number of classes to construct at the start, but we could do the initial generation from the EF Model Wizard.
The classes could then modified with any custom properties or to remove anything we don't need, rather than the EF Designer that would require us to extend any classes.
The disadvantage is that any changes to the database would have to be manually added to our classes, unlike using the designer which will allow easy updating.
Edit:
I think I was confused in this area. From reading, it appears that the correct way to do Data First is to create partial classes for all the auto generated classes, and then to make any modifications to the partial classes as part of the 'business' layer.
My thought has therefore changed from favouring the Code First from Database, to using the EF Designer to existing database and then creating the partial classes.
In any case you'll have to synchronize the EDM (entity data model) and the DB. You have to make sure that the EDM is fully compatible with your database. If not, it will fail, no matter if it's Code First or you use a Model.
The only difference is that:
using the designer you can do it graphically, and easyly set properties, column names, and so on
using Code First, you have to set these properties, columns names, data types and so on using conventions, Fluent API or attributes
With Code First the only advantage is that once you've synchronized the Code First model (see "Code First is also an EDM, but somewhat limited") and the database, you can start using Migrations, and evolve your model using them, which later makes it easier to apply changes to the production DB (whenever a new version is released). With graphic model you cannot use migrations, and have to upgrade the Db directly from Visual Studio, or creating SQL DDL scripts by hand.
Code First is also an EDM, but with a few missing functionalities
It doesn't matter if you use Code First or draw a model, an EDM (entity data model) will be generated. If you're used to design databases, probably you'll be more comfortable using the designer. Beware of the notes on EF Core (former EF7) below!.
However, the EDM generated by Code First has a few limitations that the designer doesn't have.
The most outstanding limitations of Code First is that in the designer you can easily map user defined functions from the BD, for example scalar and table value functions, and stored procedures. With Code First there are much more limitations.
in EF 6.1 most of this limitations dissapear, but it's still a bit difficult to make the mappings.(In fact, as of today, 2014, there's only a sample, and a simple Nuget package on how to do it.).
As of march 2017, non-Core EF, i.e. EF 6.1, is no longer being updated. MS will probably solve bugs if they appear, (this was wrong: but don't expect further changes)
New features appeared in 6.2: What's new in EF 6.2, which includes definition of indices with Fluent API, support for Like, support for non-identity DB generated keys, like SEQUENCE and some other changes
Changes on EF Core, former EF7 (as of may 2015)
At this time Microsoft is developing EF 7, but it's also maintaining EF 6.x. The current recommendation is to keep using EF 6 for some time, because EF 7 is not mature enough.
EF 7 is being developed from scratch to overcome the inherited ObjectContext which was posing terrible limitations to implemente new features. But it implements the most widely used DbContext with little changes. So, if you use DbContext you'll have an easy migraiton path to incoming new versions of EF.
However there is a very important change: in EF Core (former EF7) the EDM model dissapears in favor of Code First models. So, if you want to use the technology of today and assure an easy upgrade to new versions, don't use Model First or Database First: use Code First. There are important reasons for Microsoft to have taken this decision: Code First works much better in a team environmet with version control, and allows to work with Migrations. Anyway tou can still see the model in a graphical way (with Power Toools) or use a third party tool to create the model using a designer (several of the current commercial solutions will support this for EF7).
NOTE: Why is much better Code First in team environments? If several team members modify the model it's much easier to merge changes in several code files, than in a big XML file, with lots of lines which defines the model. It's also much harder to understand the changes between versions in this hugh XML file. For medium or big projects, I recommend you to move to Code First ASAP
I'm following an MSDN article on applying the Repository Pattern and the Unit Of Work Pattern to Entity Framework, but I'm stuck at the mapping between the custom-made domain models and the as-yet-nonexistant database.
The article has me create two simple POCOs, Employee and TimeCard. It also walks through creating generic repositories and custom implementations therein. (I'm using the custom repositories so I can try to keep EF dependencies in the data access assembly.) However, they sort of glaze over an important step in the mapping. The article says:
With the POCOs in place we can create an Entity Data Model (EDM) in Visual Studio (see figure 1). We will not use the EDM to generate code for our entities. Instead, we want to use the entities we lovingly craft by hand. We will only use the EDM to generate our database schema and provide the metadata EF4 needs to map objects into the database.
The "Figure 1" it references is here:
But that's all it says on the subject. There's an aside on how to generate POCOs from an EDMX. There's lots of information via Google on how to generate POCOs, generate EDMX from a database, etc. But in this walk-through we already have the POCOs and I need to use them in the EDMX which would, in turn, generate the database (I'm assuming, based on other code-first walk-throughs).
I've added an "ADO.NET Entity Data Model" to the project, which is basically a blank canvas. But I'm not seeing how to add my existing POCOs to that canvas. Do I have to re-create them manually on the design surface (which would be a pretty significant duplication problem in a larger domain)? If so, how do they map to the existing ones?
Typically when you use the designer the flow is the opposite - you create the model with the designer (or create/update the model from the database) and then the code is created for you. The created code can be either the EF1 style code with entities derived from EntityObject and attributes etc. which is created with a Single File Generator which is a part of VS (Code Generation Strategy set to "Default") or the code can be created with T4 templates (Code Generation Strategy set to "None") in which case you need to add T4 templates to your project. EF matches POCOs with Entities from the edmx file by convention (names of entities have to be the same, names and types of properties have to match etc.). In the article for some reason they went the opposite way which is weird since it requires that you create all the entities and relationships with the designer manually (since the designer does not know how to create entities from the code) and make sure that the requirements for the conventions (you may not even be aware of some of them) are met. However when you start with code the better approach is to use the EF Code First approach and skip the designer entirely. Code First can create database from your code. It also contains migrations feature which allows evolving your database along with your code. Finally (as you seem to use Visual Studio 2010) you could use EF6 which allows using all the goodness that was previously only available on .NET Framework 4.5 to be used on .NET Framework 4. See here for more details: http://entityframework.codeplex.com/
*the names are going to change in the new version designer that supports EF6 and works with Visual Studio 2012 and Visual Studio 2013
EDIT to address questions from the comment
If you would like to use Code First would use the DbContext API which is a streamlined wrapper of the ObjectContext API. Here is a walkthrough that should help get you started.
You can still use Code First if you have an existing database - the difference is that you will not be able to use migrations. The easiest way to get started with this is to use EF Power Tools. Take a look at this tutorial to see how to do that.
More help here
I have to create a new project and (as usual) is with an existing SQL Server database.
I used to use EF Code First connecting with my database, opening my EDMX model designer and then right click --> Add Code Generation Item. (http://weblogs.asp.net/jgalloway/archive/2011/02/24/generating-ef-code-first-model-classes-from-an-existing-database.aspx) Easy.
But now I've discovered there's something called EF Power Tools that allows me to do Reverse Engineer Code First (cool name!) and get the same (http://msdn.microsoft.com/en-us/data/jj200620)
Do you know the difference between the two options? Which one is better?
Thanks in advance.
(Sorry if this question was previously asked but I didn't find it.)
The difference is that the edmx approach is not code first, but database first with DbContext API. You will always use the database as the source of model changes.
EF Power Tools produce a truly code first model with DbContext: from then on you will change the class model first and modify the database accordingly (e.g. by EF migrations).
Neither is "better". DbContext API is easier to work with than ObjectContext, but both approaches use the former. It's up to you to choose whether you want to work database first or code first. It's a matter of personal preference and it may depend on who maintains the database structure. With database first it is easier to respond to changes someone else imposes on the database structure.
As far as workflow goes for database first, adding to what #Gert-Arnold said:
With database first it is easier to respond to changes someone else imposes on the database structure.
If someone else is managing the database changes, I'm finding it far easier to use the EF Designer. You get an updated database, then just right-click in the EF Designer and update the model from the database. You can use source control to easily view what has changed.
Also, if you only need a subset of tables from the database, reverse engineering causes alot of work having to go back and remove classes and properties from the context.
I found re-reverse engineering via code-first to an existing database to be just too much of a pain trying to figure out what changed and how I needed to update code that used the context.